The contribution of transpiration and respiration in water loss of perishable agricultural products: The case of pears

Transpiration and to a lesser degree respiration are two well-known processes of water loss from fresh agricultural products, associated with visual and texture degradation. Neglecting respiration as a water loss mechanism leads to erroneous results at saturation where, although the water vapour pressure deficit is zero and therefore water loss should be zero, on the contrary a finite water loss exists. In this context an experiment was set up to analyse the water loss associated with transpiration and respiration in pears ( Pyrus communis L., Kontoula ) at 0, 10 and 20 °C and 70%, 80% and 95% RH, as well as the air humidity of the cold storage. The choice of pears was based on the fact that they rank third among the most important tree fruits. The estimated transpiration rates ranged between 0.03 and 0.28 mg cm −2  h −1 for water vapour pressure deficit range of 0.0–0.52 kPa. The mean respiration rates were calculated at 0, 10 and 20 °C as 0.48 ± 0.1, 1.27 ± 0.2 and 3.48 ± 1.1 mL[CO 2 ] 100 g −1  h −1 . Quantification of the two sources of water loss showed that, close to saturation (20 °C and 95% RH), the water loss due to respiration accounts for 39% of the water loss due to water vapour pressure deficit while, on average, the water loss due to respiration accounts for 8%, 14% and 23% of the water loss due to water vapour deficit at 0, 10 and 20 °C. These findings justify why water loss due to respiration should not be neglected under certain environmental conditions.